Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates to a cutter/tool and a method for machining a surface, in particular to a method of cutting or grinding with a rotary tool.
2. Description of the Prior Art
Machining is most commonly done with ball end mills (having a hemispherical end), flat end mills (having a flat bottom), and bull-nose end mills (having a flat bottom with a fillet radius between the bottom of the tool and the shank). These cutters are generally oriented perpendicular, or close to perpendicular to the surface. In some cases, milling can also be done on the shank of the tool, which generally leaves a flat/ruled surface. The cutters described herein will allow cutting in similar modes, (i.e. basically perpendicular or parallel to the surface) as well as when the tool is neither perpendicular nor parallel to the surface, and have great flexibility in the potential modes of use. The disadvantages and inefficiencies of ball end mills are very well-known to those skilled in the art and will not be discussed here. Flat end mills leave a very rough surface when inclined and are generally only used for rough machining. Bull nose end mills are only efficient when they can be more or less normal to the surface being machined, which prevents their implementation in applications where the geometry is tightly constrained. They also generally require 5-axis machines in order to be used.
Cutters with a cutting edge described by y=f(x) where f(x) is a curve are described in U.S. Pat. Nos. 4,968,195 and 4,945,487, but the nature of f(x) curves, such as an ellipse or a parabola is fairly restrictive and these cutters have not gained acceptance. This is best explained by examining an ellipse. An elliptical cutter with a fixed set of end points cannot be modified or changed. The endpoints are factors in the defining equation of the ellipse. Thus, for a given set of endpoints, there is only one set of equations which can define that ellipse (or cutter if the ellipse is used to define a cutter). This is too restrictive for most applications, and does not offer enough efficiency gain to justify the additional programming complexity; hence, the cutters are not generally used today. A similar patent is U.S. Pat. No. 5,513,931 which describes an elliptical cutting insert, which suffers from the inherent limitations of an ellipse. U.S. Pat. No. 5,087,159 describes an end mill with a radius at the tip. This cutter is similar to a bull nose end mill in application, and efficiency is limited by the minimum radius of curvature on the milling surface. It is also restricted to applications where the cutter can be more or less perpendicular to the surface.
The nature of the apparatus is a cutting tool where at least one portion of the cutting edge is curved and has a radius of curvature larger than the radius of the tool itself. This cutting edge may have a changing radius of curvature as well. This cutting edge may be described a single curve, or a series of curves. Generally, at least one of the curves will be of a parametric form. By using multiple curves, or a parametric curve, the additional control over shape not presented by an ellipse or parabola is gained. This will allow wider implementation of said cutters because the wider range of curvatures presented not only increases efficiency, it also increases the number/types of applications that can be used.
For instance, an elliptical cutting edge with a length of 0.25 inches and a maximum radius of curvature of 4.0 inches (the larger the curvature, generally the more efficient), will have a total curvature variation along the cutting edge of less than 10%. If a surface with areas of low and high curvature is machined, the elliptical edge will be selected based on the maximum curvatures in order to avoid over-cutting. Thus, since the curvature along a practically-sized ellipse does not vary greatly, the efficiency in the areas of low curvature is degraded. However, with a combination of curves or with a parametric curve, virtually an infinite change in shape and curvature can be created even in a short length, thus increasing efficiency. A parametric curve (where x=f(t) and y=g(t)) is advantageous because (x,y) are defined independently of each other, easily enabling an infinite number of permutations. With a parametric curve or a number of curves, the curvature can easily be made to vary by 1000% even over a short length.